The decay of wood and other cellulosic materials by fungi, and the consumption of wood by termites, cause significant economic loss. Until recently, the most widely used wood preservative has been chromated copper arsenate (CCA). However, production of CCA for use in residential structures was prohibited as of January 2004 due to issues raised concerning the environmental impact and safety of arsenic and chromium used in CCA-treated lumber. As CCA replacements, arsenic-free and chromium-free wood preservatives are sought.
Various alternative approaches have been taken to incorporating copper into wood preservatives. Salts of copper and other fungitoxic metals are generally water soluble, and rapidly leach from treated wood causing loss of the preservative function. Polymeric binders can be used to retain fungitoxic and termiticidal metal complexes in wood. U.S. Pat. No. 6,843,837, for example, discloses a wood preservative containing metals complexed with a non-polymeric amine, a polyethylenimine, and ammonia together with a vinyl based polymer. Such a composition using a nonionic polymer may readily biodegrade due to colonization of wood by soil bacteria, thereby allowing leaching of the protective metal complex from the wood.
US 2004/089,196 discloses a wood preservative containing a copper complex with polymers containing amidoxime, hydroxamic acid, thiohydroxamic acid, N-hydroxyurea, N-hydroxycarbamate, or N-nitrosoalkyl-hydroxylamine that is solubilized using ammonia, ethanolamine, or pyridine.
U.S. Pat. No. 4,737,491 discloses a wood preservative containing copper and/or zinc complexes dissolved in water, and a polyacrylic acid having a molecular weight of less than 2,000, for stabilizing the metal complex in wood. The polyacrylic acid polymer copper complex is soluble in ammonia water, or forms micelles in ammonia water, and penetrates wood at least partly. It is reported by U.S. Pat. No. 4,737,491, however, that polyacrylic acid polymers with molecular weights above 2,000 have low wood penetration, which results in largely or only surface impregnation of the wood for solutions of polymers that have molecular weights above 2,000.
U.S. Pat. No. 4,409,358 discloses a crop protection agent that is a copper amine salt of a polymer or copolymer of acrylic acid and/or methacrylic acid and optionally a lower alkyl ester of acrylic acid or methacrylic acid. U.S. Pat. No. 5,242,685 discloses a crop protection agent for controlling fungi or bacteria that is an aqueous solution of a polymer acid, containing acrylic acid or methacrylic acid and optionally an acrylate or methacrylate, and at least 12% of copper, where the copper is dissolved by applying ammonia gas under pressure. The expense in making acrylic acid or methacrylic acid, and the requirement for 2 moles of monobasic (meth)acrylic acid groups per mole of Cu make this type of agent undesirable for commercial preparation.
U.S. Pat. No. 4,175,090 discloses a process for preparing a solution containing a cuprammonium complex of one or more C1 to C4 monocarboxylic acids. This type of complex would readily leach from treated wood and thus not provide a lasting preservative.
There thus remains a need for wood preservatives that are highly penetrating, effective, long lasting, and easily prepared for replacement of the CCA wood preservative.